I started out with an Eheim 2128 filter which I like. But I wanted to add a second filter. My choice was to add a Rena XP4. Since I already know I will be overstocking this tank, filtration is very important to me.
The big question for me was where to place the filter intakes and outputs! Having good filters doesn't matter if you don't create a good filtration circulation in the water. So I created a few diagrams to ask others what they thought. Nobody liked idea #1! #4 turned out to be the most popular.
I purchased two of the Customflo kits to be able to design a customized intake/output system. Each intake and output connection comes with its own flow control so you can ensure they all work together. For example, to ensure the second intake screen had enough pressure to actually suck in water, you turn the first one down. This way, both intake screens suck in the same amount of water equally.